BIONOMICS 269 



rest on Induction and Experiment. By the former is meant the fact 

 that many plants of widely different families assume the same special 

 forms under similar conditions of life; and the just inference is that 

 there is a distinct cause and effect, so that they bear "mimetic" 

 characters. Such, e.g., is well seen in the fleshy, massive stems of 

 Euphorbias, Stapelias, etc., of Africa, which resemble members of the 

 Cactus family of Mexico; and the true Aloe of Africa is just like the 

 " American Aloe " or Agave of Mexico. 



Photosynthetic plants are, in a sense, always "mimetic" 

 in that they all alike contribute in a definite manner to one 

 great cause, viz., synthetic evolution, i.e., symbiogenesis. 

 The outwardly appearing wholesome diversification in plants 

 is only, as we have seen, in keeping with the differing degrees 

 to which they have managed to perfect their productive powers 

 pari passu with their morphological complexity. 



The most vital adaptation of plants, the main theme from 

 which all others are but variations, is thus beyond any need of 

 being established by laboratory experiments. Indeed, we may 

 say that all such experiments which fail to take the funda- 

 mental bio-economic adaptations of the plant fully into account 

 must be fallacious, or can at best only yield very partial 

 results. 



Seeing that fundamentally the great bio-economic duty 

 of plants makes for one great fundamental symbiotic adapta- 

 tion (for work), it is not difficult to understand that with the 

 arrival of similar external conditions cases of "convergence" 

 may easily arise; i.e., that plants may make additional adapta- 

 tions to similar external conditions in similar ways, although 

 there may be no affinities or any relations between them 

 whatever. The very fact that one and the same (symbio- 

 genetic) theme underlies all genuine specialisation and gives 

 the direction to evolution must easily cause the variations from 

 this theme to approach one another as soon as for all of them 

 identically changed conditions arise. 



It is only those organisms that lived to no positive bio- 

 economic purpose, like the parasites, that can afford, 



